Field of the Invention
The present invention relates to a sealing device for a fuel-cell stack and to a cell and a fuel-cell stack comprising such a device.
Related Art
A proton exchange membrane fuel-cell stack is an assembly (multilayer referred to as a stack) of a given number of elementary cells.
As schematically illustrated in FIG. 8, an elementary cell generally comprises a stack that contains the following elements:                an anode plate 6 and a cathode plate 66;        a membrane electrode assembly (MEA) 5;        a sealing system 3 on the side of the fuel (hydrogen gas) supply network;        a sealing system 3 on the side of the oxidant (air) supply network; and        a system for sealing a coolant (liquid or air) supply network (not shown in FIG. 8 for the sake of simplicity).        
The stack is compressed in order, on the one hand, to seal the cells, but also in order to compress the membrane electrode assembly (MEA) to a degree of compression that is optimal for operation of the cell. The cell is generally kept under pressure by end elements or tie rods.
The cells of fuel-cell stacks require seals in order to ensure they are leak tight to various gaseous or liquid reactants and to the coolant.
These seals must respect various constraints among which:                they must be easily handleable for fitting/removal        they must be positionable with relative precision between the membrane electrode assembly and the corresponding (polar or bipolar) stack plate;        they must not contaminate the membrane electrode assembly;        they must be able to withstand the ambient environment (reactants, pressure, temperature, etc.);        etc.        
The cost of such seals must also be compatible with economic constraints.
Multiple sealing-device solutions are known for fuel-cell stacks. Thus, for example, it is known to overmold a seal directly onto the plates of a stack. It is also known to produce bipolar plates by injecting molding of the sealant. However, these solutions do not allow the membrane electrode assemblies or the sealing device itself to be easily maintained. Specifically, if the seal fails the plate with its seal must be replaced, thereby increasing maintenance cost.
Document U.S. Pat. No. 6,231,053 describes a sealing device securely fastened to a membrane electrode assembly (MEA), which comprises a rigid sheet to which a flexible seal is vulcanized, the seal also being vulcanized to the MEA.
However, this device does not satisfactorily meet the above constraints, especially as regards the ease of differentiated maintenance of the MEA and the sealing system. Specifically, if the seal fails the MEA with its seal must be replaced, thereby increasing maintenance cost. The same goes if the core of the stack fails.
Another known solution consists in providing independent flexible seals possessing fastening systems for holding them against the plates during assembly. This solution however considerably increases the time taken to fit the seal. In addition, while it is being fitted, the seal may kink, thus threatening the reliability of the fitted seal.
Industrialization of fuel-cell stack manufacturing processes and the need to decrease manufacturing costs requires the time taken to assemble such assemblies to be decreased while a satisfactory level of reliability is nonetheless guaranteed.